Ring puckering in five membered rings: The microwave spectrum,dipole moment and barrier to pseudorotation in 1,3-dioxolane

The microwave spectrum of 1,3-dioxolane was investigated in the region 8–35 GHz. Nine vibrational states were assigned which indicated that the molecule undergoes pseudorotation. The dipole moment for each vibrational state was measured and found to be constant within experimental error at 1.19 ± 0.03 D. The lowest energy pair of vibrational states were found to be connected by rotation vibration transitions. The splitting of this pair was found to be 64 840.65 MHz with a perturbation element 435 ± 30 MHz. From the variation in the rotational constants, the far-infrared data, and the v = 0, 1 splitting the Hamiltonian for pseudorotation was found. Hφ=3.99Pφ±5.1(1-cosφ)?20.01(1?cos2φ).The phase of the potential function was determined from relative intensity measurements to be such that the maximum in the potential energy is at the twisted configuration with the bent configuration being 10.2 cm^?1 lower in energy.     

Raman analysis of synthetic eritadenine

Eritadenine, 2(R),3(R)‐dihydroxy‐4‐(9‐adenyl)‐butyric acid, is a cholesterol‐reducing compound naturally occurring in the shitake mushroom (Lentinus edodes). To identify the unknown Raman spectrum of this compound, pure synthetic eritadenine was examined and the vibrational modes were assigned by following the synthesis pathway. This was accomplished by comparing the known spectra of the starting compounds adenine and D ‐ribose with the spectra of a synthesis intermediate, methyl 5‐(6‐Aminopurin‐9H‐9‐yl)‐2,3‐O‐isopropylidene‐5‐deoxy‐β‐D ‐ribofuranoside (MAIR) and eritadenine. In the Raman spectrum of eritadenine, a distinctive vibrational mode at 773 cm⁻¹ was detected and ascribed to vibrations in the carbon chain, ν(C C). A Raman line that arose at 1212 cm⁻¹, both in the Raman spectrum of MAIR and eritadenine, was also assigned to ν(C C). Additional Raman lines detected at 1526 and at 1583 cm⁻¹ in the Raman spectrum of MAIR and eritadenine were assigned to ν(N C) and a deformation of the purine ring structure. In these cases the vibrational modes are due to the linkage between adenine and the ribofuranoside moiety for MAIR, and between adenine and the carbon chain for eritadenine. This link is also the cause for the disappearance of adenine specific Raman lines in the spectrum of both MAIR and eritadenine. Several vibrations observed in the spectrum of D ‐ribose were not observed in the Raman spectrum of eritadenine due to the absence of the ribose ring structure. In the Raman spectrum of MAIR some of the D ‐ribose specific Raman lines disappeared due to the introduction of methyl and isopropylidene moieties to the ribose unit. With the approach presented in this study the so far unknown Raman spectrum of eritadenine could be successfully identified and is presented here for the first time. Copyright © 2008 John Wiley & Sons, Ltd.     

Laser Stark and laser microwave double resonance spectroscopy of fluoroacetylene with the CO2 laser

The CO₂ laser Stark spectrum of fluoroacetylene was identified for the ν₃, ν₃ + ν₄ ? ν₄, and ν₃ + ν₅ ? ν₅ vibrational bands. The origins of these bands were precisely determined (±0.0003 cm^?1) to be 1061.4452, 1059.0639, and 1064.6960 cm^?1. A CO₂ laser microwave double resonance experiment in the presence of the Stark field is described. This technique was applied to assignment of the Stark spectrum, calibration of the Stark electrode spacing, and precise determination (±0.0003 D) of dipole moment. The dipole moments of the HCCF molecule in the ground, ν₃, ν₄, ν₅, ν₃ + ν₄, and ν₃ + ν₅ vibrational states are 0.7207, 0.7447, 0.6557, 0.7441, 0.6769, and 0.7689 D.     

The intensity distribution in the CH(A2Δ − X2Π) spectrum produced by electron impact on acetylene

The intensity distribution in the rotational and vibrational structure of the CH(A²Δ ? X²Π) spectrum, formed by dissociative excitation of acetylene by electron impact, is analysed. This spectrum is built-up from three overlapping bands, namely, the 0-0, 1-1 and 2-2 bands. The intensity distribution in the rotational structure of the 0-0 band is determined by an analysis of the free rotational lines of the R-branch. The intensity distribution in the other bands is analysed by a comparison of the spectrum with a spectrum simulated on the computer. In this way, the overlap of the various rotational and vibrational transitions is taken into account. It turns out that the distribution of molecules over the rotational levels can be described by assuming one Boltzmann distribution for each vibrational level.     

Microwave spectrum,structure, and dipole moment of 7-oxabicyclo[2.2.1]heptane

The microwave spectrum of 7-oxabicyclo[2.2.1]heptane has been assigned in the ground and two excited vibrational states. Relative intensity measurements indicate that these two vibrations have wavenumbers of 120(30) and 330(30) cm^?1. The dipole moment obtained from Stark effect measurements is 1.621(10) D. The molecule is shown to have C_2v symmetry and the assignment of the two singly substituted ¹³C species gives the following skeletal structure: C₁-C₂ = 1.537(5) Å; C₂-C₃ = 1.551(5) Å; C₁-O = 1.452(10) Å; ?C₁OCC₄ = 95.3(10)° φ = 113.1(5)°.     

Electronic transition-moment variation in the A1π-X1Σ system of the GeO molecule

The spectrum of GeO was excited in a carbon arc and the relative band intensities were measured by using photographic photometry and were then interpreted in terms of Franck-Condon factors. It was found that the electronic transition moment varies as Re(r)=constant×(1-0.476r-0.061r²), where 1.62?r, Λ?1.82. Using this relation, smoothed band strengths, band-oscillator strengths and Einstein coefficients of the bands were calculated using expressions given by Penner. The effective vibrational temperature is estimated to be 1090 K. The average life times of the v′=0 and 1 vibrational levels have also been estimated.     

The microwave spectrum of 14NH3 in the v = 000011 state

The frequencies and assignments of 50 lines in the pure inversion spectrum of ¹⁴NH₃ in the 0001¹ vibrational state are reported in the microwave frequency region 18–53 GHz and in selected regions up to 58 GHz.The J = 0 inversion frequency, K-type doubling constant K, l = 2, ?1 and molecular dipole moment in this state are 32 904.7 ± 2.0 MHz, 1.958 ± 0.040 MHz and 1.459 ± 0.002 D, respectively, where model inadequacies are included in the uncertainties of the first two parameters. The dipole moment measurements for this and the ground state are in excellent agreement with Stark laser measurements. An expression containing the effective l-type doubling constant is obtained from the combination of frequencies $\text{[ν(1, 1, 1) ? ν(1, 1, ?1) ? ν(2, 1, 1) + ν(2, 1, ?1)]}\text{8}\text{= 10 361.894 ± 0.004}\text{MHz}$. A preliminary value for the l-type doubling constant is 10 655 ± 20 MHz.     

Theoretical integrated intensities for the 2ν2 and 2ν2-ν2 bands of HCN and DCN

Dipole moment functions, both perpendicular and parallel to the molecular axis, are calculated from the SCF and MRD-CI results of a previous study for the normal ν₂ bending vibrations of HCN and DCN. Vibrationally averaged dipole moments and the infrared transition matrix elements are then obtained from the dipole moment functions and vibrational wave functions. MRD-CI results, with known experimental values in parentheses, for HCN are 〈0|μ|0〉 = ?2.954(?2.985) D, 〈1|μ|1〉 = ?2.915(±2.942) D, 〈0|μ|1〉 = 0.148(0.147) D, 〈0|μ|2〉 = ?0.027 D, 〈1|μ|2〉 = 0.210 D. Calculated absolute intensities at 1 atm and 0°C for the (02⁰0) ← (000), (02⁰0) ← (010), and (02²0) ← (010) bands of HCN are 25 (40 ± 10 as estimated from spectra), 8.5, and 17.0 atm^?1 cm^?2, respectively. Results for DCN are also reported.     

On the nature of a lattice vibrational mode at a frequency of 135 cm−1 in Hg1 − x Cd x Te alloys

The vibrational spectrum of a cadmium impurity atom in the HgTe crystal has been calculated using the microscopic theory of lattice dynamics in the approximation of a low impurity concentration. Within this theory, the behavior of the local and quasi-local modes induced upon substitution of the lighter Cd atom for the Hg atom in the region of the zero or very low one-phonon density of states in the HgTe crystal has been considered. It has been found that, apart from the local mode at a frequency of 155 cm^?1, the calculated vibrational spectra exhibit a weak (but clearly pronounced) feature at a frequency of 134 cm^?1, which coincides with the experimentally observed vibrational mode (the “minicluster” mode) at a frequency of 135 cm^?1 in the Hg_{1 ? x} Cd _x Te (x = 0.2–0.3) alloys at 80 K.     

The 290-nm absorption system of propiolyl fluoride

The vapor-phase absorption spectrum of propiolyl fluoride HCCCOF and deuterio-propiolyl fluoride has been examined under medium resolution in the region from 303 to 260 nm. While considerable vibrational structure is evident, all bands are found to be rotationally diffuse. The electronic transition is identified as the singlet-singlet $\text{π}{}^1\text{← n}$ transition analogous to the 382-nm system of propynal. The evidence for a nonplanar excited-state geometry is discussed. The principal excited-state vibrational frequencies identified are 158 (ν′₉), 396 (ν′₈), and 1222 cm^?1 (ν′₃) for HCCCOF. The corresponding values for DCCCOF are 150, 390, and 1217 cm^?1, respectively. The triplet ← singlet system involving the same electron promotion has not been found.     

The rotational spectra of the υ8 = υ9 = 1 and υ6 = υ7 = 1 interacting vibrational states of nitric acid (HNO3)

The analysis of the rotational spectrum of HNO₃ has been extended to include the υ₈ = υ₉ = 1 state at 1205.7 cm⁻¹ and the υ₆ = υ₇ = 1 state at 1223.4 cm⁻¹. Based on 78-519 GHz data, the assignments in the 8¹9¹ vibrational state have been significantly expanded from the previously reported microwave measurements [T.M. Goyette, F.C. De Lucia, J. Mol. Spectrosc. 139 (1990) 241-243]. A new microwave analysis is also reported for the 6¹7¹ vibrational state. A simultaneous analysis takes into account the localized ΔK_a = ±2 Fermi resonances between the vibrational states, describes the torsional splitting of 3.3 and 1.4 MHz for the 8¹9¹ and 6¹7¹ states respectively, and fits to experimental accuracy over 1500 rotational transition frequencies that extend up to J = 59. Infrared energy levels [A. Perrin, J.-M. Flaud, F. Keller, A. Goldman, R. D. Blatherwick, F. J. Murcray, C. P. Rinsland, J. Mol. Spectrosc. 194 (1999) 113-123] were also included in the analysis and fit to experimental accuracy. Measurement of strongly perturbed transitions in each vibrational state provide a determination of the band origin difference of 17.733184(17) cm⁻¹. The rotational constants agree well with those predicted by vibrational-rotational constants of the fundamental modes. Furthermore, the analysis will provide a very accurate simulation of the infrared spectrum of HNO₃ in the 8.3 μm region.     

溴乙烷分子的质量分辨阈值光谱

利用单色双光子(1C2P)技术得到了高精度的溴乙烷分子的质量分辨阈值(MATI)光谱，精确给出了溴乙烷分子的绝热电离势和离子振动频率.从中性基态到离子基态两个自旋-轨道分量X₁ ²E_1/2和X₂ ²E_1/2的绝热电离势分别为83097±3 cm^-1和85452±3 cm^-1，离子基态两个自旋-轨道分量的间隔为2355±6 cm^-1，这些值与文献报道值符合得较好，且精度更高.溴乙烷分子的单色双光子质量分辨阈值光谱展现出丰富的振动结构，这是在溴乙烷分子相继吸收两个光子的过程中波包在解离态势能面上演化的结果.以已有的离子振动谱标识为参考，以中性分子的振动频率为基础，标识了溴乙烷分子的质量分辨阈值光谱，发现观测到的振动模几乎都和溴乙烷分子的解离运动有关，其中还包括一些非全对称模. 关键词： 质量分辨阈值光谱 振动模 单色双光子零动能光谱技术 溴乙烷     

Study of anharmonic effects in the IR spectrum of a solution of CF<Subscript>3</Subscript>Br in liquid argon

The vibrational spectrum of CF₃Br with the natural abundance ratio of isotopologues is studied in solutions in liquid Ar at T = 90 K in the frequency range 4000–400 cm^?1 with a resolution of 0.1 cm^?1 for the concentration range 3.1 × 10^?7?6.3 × 10^?3 mol %. The parameters of the vibrational spectrum of the molecule are determined: the frequencies are measured accurate to ± 0.1 cm^?1, and the transition probabilities are found up to the fourth order inclusive. One hundred fifty absorption bands of CF₃Br are interpreted, including the bands belonging to all the isotope modifications of this compound; the halfwidths of these bands are determined. For all the fundamental frequencies, the isotope shifts are obtained. Vibrational ?-resonance is studied. Using the experimental data obtained and taking into account this resonance, a complete set of parameters describing the experimental frequencies with the error δ ≈ 0.3 cm^?1 was found. This set consists of 6 harmonic frequencies and 30 anharmonicity constants, including the constants r _ik related to vibrational ?-resonances.     

Submillimeter wave spectrum and molecular constants of N2O

The submillimeter wave spectrum of the N₂O molecule has been investigated within the 375–565 GHz frequency range with a sensitivity better than 10^?8 cm^?1. The measured frequencies include 161 lines with intensities γ ? 10^?6 cm^?1 belonging to 22 spectroscopically different species of the molecule (specifically, the ground and some excited vibrational states of the five most abundant isotopic species of the molecule in natural abundance) with a statisticall and systematic error of the order of magnitude 10^?8. Rotational and two centrifugal stretching constants could be determined for each spectroscopic species. For each isotopic species observed, we have made a general analysis of the spectrum in different vibrational states bearing in mind resonance effects. The total number of the rotational and rovibrational constants obtained exceeds 40.     

The H2O spectrum between 4200 and 5000 cm−1

The spectrum of water vapor heated in an absorption cell at 60°C has been recorded on a Fourier transform spectrometer between 4200 and 5000 cm^?1. A thorough analysis of the spectrum has been performed, leading to an improved and extended set of rotational energy levels for the (030) vibrational state. Intensities of about 50 lines of the 3ν₂ band are reported and a calculation of these intensities has been performed allowing the determination of the vibrational matrix element of the transformed dipole moment operator.     

Spectrum of water vapor between 8050 and 9370 cm−1

Measurements of the line positions of H₂¹⁶O in the 8050 to 9370 cm^?1 region have been performed at a spectral resolution of 0.07 cm^?1. A grating spectrum of room-temperature water vapor and a Fourier transform spectrum of heated water vapor (T ? 60°C) were used in the interpretation. A careful analysis of the bands ν₁ + 3ν₂, 3ν₂ + ν₃, 2ν₁ + ν₂, ν₁ + ν₂ + ν₃, and ν₂ + 2ν₃ has led to a set of rotational levels belonging to the vibrational states (130), (031), (210), (111), and (012). Many vibrorotational resonances were detected.     

Electronic transition of C3H− in the vicinity of the lowest photodetachment threshold

The electronic spectrum of the C³H(D)^? anion has been studied near the lowest electron detachment threshold associated with the chain isomer. On the basis of the vibrational and rotational analyses, the photodetachment spectrum is assigned to the ³A″ ← [Xtilde]³A″ electronic transition of the cumulene-like C³H(D)^? anion. The spectrum is characterized by a rich vibrational structure leading to the determination of almost all fundamental frequencies. The vibrational progression involving the CCH(D) in plane bending mode (V¹ ₆) is fitted with a 1-dimensional potential energy curve along the CCH(D) angle. This fit and the rotational analysis enable the geometry of the upper state to be determined. Although this excited state is expected to have dipole bound character, its neutral counterpart has a significantly different structure. The observation of an excited triplet state near the electron detachment threshold and close to the the calculated transition state for the electron catalysed isomerization reaction leads to new insight into this process.     

Microwave spectrum,dipole moment,and structure of 3-aminopropanol

The microwave spectra of 3-aminopropanol and three of its deuterium substituted isotopic species have been investigated in the 26.5 to 40 GHz frequency region. The rotational spectrum of only one conformer has been assigned in which presumably a hydrogen bond of the OH---N type exists. The rotational spectra of a number of excited vibrational states have been observed and assignments made for some of these excited states. The average intensity ratio for the rotational transitions between the ground and excited vibrational states indicates that the first excited state is about 120 cm^?1 above the ground state.and the next higher state is roughly 200 cm^?1 above the ground vibrational state. The dipole moment was determined from the Stark effect measurements to be 3.13 ± 0.04 D with its principal axes components as |μ_a| = 2.88 ± 0.03 D, |μ_b| = 1.23 ± 0.04 D and |μ_c| = 0.06 ± 0.01 D. The possibility of another conformer where the hydrogen bond could be of NH---O type was explored, but the spectra of such a conformer could not be identified.     

Microwave spectrum and structure of methyl phosphonic difluoride

The rotational spectrum of methyl phosphonic difluoride has been reinvestigated using a pulsed-molecular-beam Fabry-Perot cavity microwave spectrometer. The enhanced resolution of the Fourier transform microwave (FTMW) spectrometer (compared to the original work done in a conventional Stark spectrometer) has allowed the measurement of small A-E splittings of many of the rotational transitions caused by the internal rotation of the methyl top. The barrier to internal rotation, V₃ = 676 (25) cm⁻¹, has been determined experimentally from the A-E splittings of the rotational transitions in the ground vibrational state. This barrier height is substantially lower than the previously determined value for the barrier, which was 1252 (14) cm⁻¹. High-level ab initio calculations at the MP2/aug-cc-pVTZ level predict a barrier to internal rotation of 638 cm⁻¹, in agreement with the experimentally determined value found here. The high sensitivity of the FTMW spectrometer has also permitted the measurement of the ¹³C and ¹⁸O isotopomers in natural abundance. The addition of these two isotopomers has allowed an improved structural determination.     

The study of ungerade electronic states of the Xe2 molecules in the region of Xe*(5p 56p, 5d, 7s, 6d) by the resonance multiphoton ionization method

Electronic spectra of the Xe2 molecules in the energy range of 77700?C89300 cm^?1 are recorded. The method of resonance enhanced multiphoton ionization of molecules in a supersonic molecular beam was used, in which excitation of the molecules by three photons was followed by ionization caused by a fourth photon (the (3+1) REMPI method). Analysis of the vibrational structure of observed systems of bands yielded information about the dissociation energy and the molecular constants for ungerade states of molecules. On the basis of the Franck-Condon principle, the equilibrium distances for potential curves were estimated from the relative intensities in vibrational progressions. Data on 16 new electronic states of diatomic xenon molecules with the dissociation limits Xe ₂ ^* ?? XE(5p ^{6 1} S ₀) + Xe*(5p ⁵6p,5d, 7s, 7p) were obtained.